771 research outputs found
Recent tests for the statistical parton distributions
We compare some recent experimental results obtained at DESY, SLAC and
Jefferson Lab., with the predictions of the statistical model, we have
previously proposed. The result of this comparison is very satisfactory.Comment: 12 pages, 6 eps figures, version to appear in Mod. Phys. Lett.
Sea-quark flavor asymmetry in the nucleon from a relativistic analysis of the Drell-Yan scattering off nuclei
It is shown that accounting for the relativistic structure of the deuteron
allows to explain the ratio of the Drell-Yan pair production cross-section at
the low Bjorken off the deuteron and the proton. Thus, the sea quark
distributions in the nucleon should be studied with accounting for the effects
of the relativistic structure of the deuteron. The suggested approach reduces
theoretical uncertainty in extracting the ratio from the data
and it is important for the clarification of the nature of the sea quark
asymmetry in the nucleon.Comment: 4 pages, 1 figures, Chiral Symmetry in Hadron and Nuclear Physics
November 13-16, 2007, Osak
Catalytic intramolecular hydroamination of aminoallenes using titanium and tantalum complexes of sterically encumbered chiral sulfonamides
Catalysis using earth abundant metals is an important goal due to the relative scarcity and expense of precious metal catalysts. It would be even more beneficial to use earth abundant catalysts for the synthesis of common pharmaceutical structural motifs such as pyrrolidine and pyridine. Thus, developing titanium catalysts for asymmetric ring closing hydroamination is a valuable goal. In this work, four sterically encumbered chiral sulfonamides derived from naturally occurring amino acids were prepared. These compounds undergo protonolysis reactions with Ti(NMe₂)₄ or Ta(NMe₂)₅ to give monomeric complexes as determined by both DOSY NMR and X-ray crystallography. The resulting complexes are active for the ring closing hydroamination hepta-4,5-dienylamine to give a mixture of tetrahydropyridine and pyrrolidine products. However, the titanium complexes convert 6-methylhepta-4,5-dienylamine exclusively to 2-(2-methylpropenyl)pyrrolidine in higher enantioselectivity than those previously reported, with enantiomeric excesses ranging from 18–24%. The corresponding tantalum complexes were more selective with enantiomeric excesses ranging from 33–39%
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